1. Field of the Invention
The invention relates to a lithium secondary battery, and more particularly, a lithium secondary battery comprising a cathode having a spinel-structured lithium-manganese complex oxide as the active material.
2. Description of the Related Art
Portable and cordless electronic appliances are becoming increasingly popular. As the power source for such electronic appliances, there is a great demand for small-sized and lightweight secondary batteries having a high energy-density. Lithium secondary batteries comprising a non-aqueous electrolytic solution have been put to practical use to meet such demands.
In general, a lithium secondary battery includes a cathode having a lithium-containing compound as the active material, an anode having a material capable of absorbing and desorbing lithium such as a carbon material or lithium metal as the active material, and a separator containing a non-aqueous electrolytic solution or a solid electrolyte. The lithium-containing compound for the active material of the cathode may include, for example, LiCoO.sub.2, LiNiO.sub.2 and LiMn.sub.2 O.sub.4 which are now under study. Recently, attention is drawn to a spinel-structured lithium-manganese complex oxide, such as typically LiMn.sub.2 O.sub.4, since the complex oxide may have a high oxidation-reduction potential and since the raw materials for the complex oxide are inexpensive and therefore a stable supply of the complex oxide is expected. In that situation, various lithium secondary batteries comprising the complex oxide as the cathode active material have been proposed.
For example, Japanese Patent Application Laid-Open No. 6-333562 discloses a lithium secondary battery comprising an LiMn.sub.2 O.sub.4 -type compound as the cathode active material, in which the compound is in the form of spherical particles having uniformly-roughened surfaces and having a particle size range of from 0.1 to 1.1 micrometer and a median diameter of from 0.5 to 0.6 micrometer. Japanese Patent Application Laid-Open No. 8-69790 discloses a lithium secondary battery comprising a lithium-manganese complex oxide as the cathode active material, in which the complex oxide has a specific surface area of from 0.05 to 5.0 m.sup.2 /g.
However, the conventional lithium secondary batteries comprising such a spinel-structured lithium-manganese complex oxide as the active material are not yet satisfactory with respect to the battery capacity and the charge-discharge cycle characteristics.
Accordingly, the object of the present invention is to provide a lithium secondary battery having high capacity and excellent charge-discharge cycle characteristics.